The present disclosure is related to systems and methods for the laser processing of materials. More particularly, the present disclosure is related to systems and methods for the singulation and/or cleaving of wafers, substrates, and plates that might contain passive or active electronic or electrical devices created thereon.
In the process, the filament is forced to curve in a profile to form a facet with a C-shaped in cross-section profile. There is huge demand in the brittle material industry to singulate samples with a C-shaped in cross-section facet profile. The C-shaped in cross-section facet profile is sometimes referred to herein as a C-cut facet profile, a C-shaped (curved) facet profile, a C-shaped facet path, a C-cut facet or just a C-cut.
Singulation of a wafer, substrate or plate having a C-cut facet profile is performed in a single scan.
In current manufacturing, the singulation, dicing, scribing, cleaving, cutting, and facet treatment of wafers or glass panels is a critical processing step that typically relies on diamond or conventional, ablative or breakdown (stealth) laser scribing and cutting, with speeds of up to 30 cm/sec for displays as an example.
In the diamond cutting process, after diamond cutting is performed, a mechanical roller applies stress to propagate cracks that cleave the sample. This process creates poor quality edges, microcracks, wide kerf width, and substantial debris that are major disadvantages in the lifetime, efficiency, quality, and reliability of the product. The sharp edges on the top and bottom surfaces are the source of potential chipping and crack development that can cause material to break apart into pieces during transportation. Generally edges are ground to remove any sharpness and this process is known as the C chamfer grinding process or step. The C chamfer grinding step is an extra processing step which necessitates additional cleaning and polishing steps. The process uses de-ionized water to run the diamond scribers and grinders and the technique is not environmentally friendly since the water becomes contaminated and requires filtration. Grinders and water refining and filtration systems also occupy valuable manufacturing space.
Laser ablative machining has been developed for singulation, dicing, scribing, cleaving, cutting, and facet treatment, to overcome some of the limitations associated with diamond cutting. Unfortunately, known laser processing methods have disadvantages, particularly in transparent materials, such as slow processing speed, generation of cracks, contamination by ablation debris, and moderated sized kerf width. Furthermore, thermal transport during the laser interaction can lead to large regions of collateral thermal damage (i.e. heat affected zones).
Laser ablation processes can be improved by selecting lasers with wavelengths that are strongly absorbed by the medium (for example, deep UV excimer lasers or far-infrared CO2 laser). However, the aforementioned disadvantages cannot be eliminated due to the aggressive interactions inherent in this physical ablation process. This is amply demonstrated by the failings of UV processing in certain LED applications where damage has driven the industry to focus on traditional scribe and break followed by etch to remove the damaged zones left over from the ablative scribe or the diamond scribe tool, depending upon the particular work-around technology employed.
Alternatively, laser ablation can also be improved at the surface of transparent media by reducing the duration of the laser pulse. This is especially advantageous for lasers that are transparent inside the processing medium. When focused onto or inside transparent materials, the high laser intensity induces nonlinear absorption effects to provide a dynamic opacity that can be controlled to accurately deposit appropriate laser energy into a small volume of the material as defined by the focal volume. The short duration of the pulse offers several further advantages over longer duration laser pulses such as eliminating plasma creation and therefor plasma reflections thereby reducing collateral damage through the small component of thermal diffusion and other heat transport effects during the much shorter time scale of such laser pulses.
Femtosecond and picosecond laser ablation therefore offer significant benefits in machining of both opaque and transparent materials. However, in general, the machining of transparent materials with pulses even as short as tens to hundreds of femtoseconds is also associated with the formation of rough surfaces, slow throughput and micro-cracks in the vicinity of laser-formed kerf, hole or trench that is especially problematic for brittle materials like alumina (Al2O3), glasses, doped dielectrics and optical crystals. Further, ablation debris will contaminate the nearby sample and surrounding devices and surfaces. Recently, multi-pass stealth dicing has been disclosed. In this approach each scan creates voids of about 50 μm long and by rotation of the incident beam and changing the focus of the laser, multiple facet C-cuts are performed. This approach suffers from the need to make multiple passes and precise rotation of the laser head and focus changes for each C-cut and therefore results in low processing throughput.
Short duration laser pulses generally offer the benefit of being able to propagate efficiently inside transparent materials, and locally induce modification inside the bulk by nonlinear absorption processes at the focal position of a lens. However, the propagation of ultrafast laser pulses (>5 MW peak power) in transparent optical media is complicated by the strong reshaping of the spatial and temporal profile of the laser pulse through a combined action of linear and nonlinear effects such as group-velocity dispersion (GVD), linear diffraction, self-phase modulation (SPM), self-focusing, multiphoton/tunnel ionization (MPI/TI) of electrons from the valence band to the conduction band, plasma defocusing, and self-steepening.
These effects play out to varying degrees that depend on the laser parameters, material nonlinear properties, and the focusing condition into the material.
Although laser filamentation processing has been successful in overcoming many of the limitations associated with diamond cutting, as mentioned above, new demands for chamfer C cutting encouraged invention of new methods and structure to successfully implement filamentation photoacoustic compression scribing using curved filaments.